A simple nanosecond spark source (Nanospark) has been constructed from several small ceramic capacitors, one thyratron and one coaxial cable. During operation, a 500-1400 pF capacitor in the spark head is pulse-charged in about 60 ns with automatic preionization from a high-voltage pulse generator switched by a thyratron. This charge is available for discharge when the gas breakdown starts. The preionization is useful to start the gas breakdown easily and to decrease the pulse-to-pulse time jitter. This Nanospark produces 12-30 ns (FWHM) light pulses with a time jitter of less than 60 ns when perated at 6-14 kV and in air of atmospheric pressure. The initiation of the spark gap is highly reliable and the radiation channel is very stable. The spark has adequately exposed customary ASA 100 film in various schlieren and shadowgraph systems and some shock wave visualizations have been obtained. In colour schlieren systems, however, high-sensitivity colour films of ASA 1600 were needed.Some
… More features of the described spark source can be improved and enhanced by pressurizing the gap : in a slightly modified version of the source, the spark can be initiated in practically any gas of almost arbitrary pressure. The light intensity and the pulse width increase with the gas pressure. If the pulse width is of but minor consequence, the quantity of radiation can be increased tenfold with a Xe-filled chamber. The spectral study showed that the light intensity with Xe-gas increases somewhat toward the infrared region. In this way we obtained colour schlieren photographs with ASA 400 films.The described light sources, due to their novel preionization technique and their practical design, fulfill the requirements for being employed in optical short duration measurements, particularly in visualization of high speed phenomena. The light output is sufficient for high quality single-shot photography making these sources at least equivalent if not superior to comparable commercially available equipment.ロ)パルス幅を短くするため、放電回路は同軸とし、放電コンデンサ-はパルス充電する。ハ)確実に放電させるため、主電極間を予備電離する。試作されたスパ-ク光源装置の性能は大気中で次の通りである。1)発光パルス幅:12ー30ns(放電コンデンサ-の大きさによる) 2)立ち上がり時間:3ー4ns 3)タイムジッタ-:60ns以下 4)トリガ-から発光までの遅れ時間:約1μs 5)光度:800ー10000W/sr以上(ASA100フィルムを完全露光)次に計11種のガスを用いて発光出力特性、パルス幅特性を比較・検討した結果、次のことが判明した。1.いずれのガスでも圧力の増加につれて発光出力は増大するが最高発光出力に大差はない。2.発光パルス幅はまた圧力と共に増大する。貴ガスのパルス幅は圧倒的に大きい。 最後に試作した大気スパ-ク光源を用い、シュリ-レン法、カラ-シュリ-レン法、シャドウグラフ法などの各種光学手法により高速現象の可視化を試み、次の様な結果が得られた。1.シュリ-レン法ではASA100の普通フィルム上に鮮明な衝撃波現象を捕えることができた。2.同上現象を三色フィルタ-を用いてカラ-シュリ-レン撮影したところ、ASA1600フィルムには鮮明に写ったが、ASA400では光量不足で、そのためXeガスを使用すれば良いことが分かった。以上の結果、本試作光源は単発撮影にも十分な発光強度を持ち、高速現象を高分解能で観測するのに大いに役立つこと、更に高感度フィルムを使用すればカラ-シュリ-レン法にも適用できることが判明した。 Less